Low-force pumping segment

ABSTRACT

A pumping segment having a low shut-off force is disclosed. The pumping segment includes a tube having an interior surface with at least two notches on opposite sides of the interior surface.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/597,094, filed May 16, 2017, which is acontinuation application of U.S. patent application Ser. No. 13/228,311,filed Sep. 8, 2011, now issued as U.S. Pat. No. 9,683,562, all of whichare hereby incorporated by reference in its entirety for all purposes.

BACKGROUND Field

The present disclosure is related to infusion pumps and, in particular,to the tubing used in the intravenous (IV) sets that are used withinfusion pumps.

Description of the Related Art

Patients in hospitals are often provided with medical fluids that areadministered through an IV infusion. Many infusion pumps operate using aperistaltic mechanism having a series of compressor blocks, or fingers,that sequentially compress and release segments of a flexible tube thatis part of the IV set, commonly referred to as the “pumping segment” ofthe IV set, connecting the source of medical fluid, such as an IV bag,to the patient. This type of mechanism relies on the resilience of thetube to expand the tube when the compressive force is removed, therebyincreasing the cross-sectional area of the tube under that finger.

Selection of a tube material having the flexibility to withstandrepeated compressions while also having the necessary resilience torebound between compressions as well as low gas permeability, tominimize the amount of air introduced into the fluid within the tube, isa challenge. A typical round tube must be compressed beyond the point atwhich the interior wall touches in order to completely close off thetube. This “overcompression” of the tube requires a significantapplication of force by the pump as well as creating additional stressin the tube walls as they are stretched during the overcompression. Onecommonly selected tube material is silicone, although silicone isrelatively expensive and has a relatively high gas permeability.

SUMMARY

It is desirable to provide a pumping mechanism that can be used in aperistaltic-type of pump that requires less force, compared to existingsystems, to completely close off the pumping segment. It would beadvantageous if this low-force pumping segment were backwards compatiblewith existing peristaltic pumping mechanisms.

In certain embodiments, a pumping segment with a low shut-off force isprovided. The pumping segment includes a tube having an interior surfacewith at least two sharp notches on opposite sides of the interiorsurface.

In certain embodiments, an IV set with a low shut-off force is provided.The IV set includes a tube having an interior surface with at least twosharp notches on opposite sides of the interior surface. Each notch hasa tip. The notches divide the tube into upper and lower portions.

In certain embodiments, an IV pump configured to provide a low shut-offforce is disclosed. The IV pump is configured to accept a pumpingsegment having an interior surface and at least two sharp notches onopposite sides of the interior surface. Each notch has a tip and thenotches divide the tube into upper and lower portions having respectiveconstant wall thicknesses between the tips. The IV pump is furtherconfigured to compress the upper and lower portions to a combinedthickness that is approximately equal to a sum of the thicknesses of theupper and lower portions of the pumping segment.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide furtherunderstanding and are incorporated in and constitute a part of thisspecification, illustrate disclosed embodiments and together with thedescription serve to explain the principles of the disclosedembodiments. In the drawings:

FIG. 1A illustrates a patient receiving an infusion of a medical fluidthrough an IV pump according to certain aspects of the presentdisclosure.

FIG. 1B depicts an exemplary IV set according to certain aspects of thepresent disclosure.

FIGS. 2A and 2B are a perspective view and a cross-section view,respectively, of a peristaltic pumping mechanism according to certainaspects of the present disclosure.

FIG. 3 is a perspective view of a standard round tube as used inexisting IV sets.

FIGS. 4A and 4B are cross-sectional views of the tube of FIG. 3 beingmanipulated by one of the peristaltic pumping fingers of FIGS. 2A and2B.

FIG. 5A is a cross-sectional view of a low-force pumping segmentaccording to certain aspects of the present disclosure.

FIGS. 5B and 5C are cross-sectional views of the pumping segment of FIG.5A being manipulated by one of the peristaltic pumping fingers of FIGS.2A and 2B according to certain aspects of the present disclosure.

FIG. 6 is another embodiment of a low-force pumping segment according tocertain aspects of the present disclosure.

FIG. 7 is another embodiment of a low-force pumping segment according tocertain aspects of the present disclosure.

DETAILED DESCRIPTION

The following description discloses embodiments of a low-force pumpingsegment suitable for incorporation into an IV set intended for use witha peristaltic IV pump. In the following detailed description, numerousspecific details are set forth to provide a full understanding of thepresent disclosure. It will be apparent, however, to one ordinarilyskilled in the art that embodiments of the present disclosure may bepracticed without some of the specific details. In other instances,well-known structures and techniques have not been shown in detail so asnot to obscure the disclosure. The systems and methods disclosed hereinare discussed in the context of a medical fluid being administered to apatient via infusion in a healthcare facility. Nothing herein should beinterpreted to limit the coverage of the claims to a healthcareenvironment or to medical treatment unless specifically stated as such.

The detailed description set forth below is intended as a description ofvarious configurations of the subject technology and is not intended torepresent the only configurations in which the subject technology may bepracticed. The appended drawings are incorporated herein and constitutea part of the detailed description. The detailed description includesspecific details for the purpose of providing a thorough understandingof the subject technology. However, it will be apparent to those skilledin the art that the subject technology may be practiced without thesespecific details. In some instances, well-known structures andcomponents are shown in block diagram form in order to avoid obscuringthe concepts of the subject technology. Like components are labeled withidentical element numbers for ease of understanding.

FIG. 1A illustrates a patient 10 receiving an infusion of a medicalfluid through an IV pump 30 according to certain aspects of the presentdisclosure. The IV pump 30 comprises a controller 32 and two pumpmodules 34. An IV set 20 is connected between a container 36 of themedical fluid and the patient 10. The IV set 20 is described in greaterdetail with respect to FIG. 1B.

FIG. 1B depicts an exemplary IV set 20 according to certain aspects ofthe present disclosure. The IV set 20 includes a combined bag spike anddrip chamber 22 configured to connect to a standard IV bag (not shown inFIG. 1B). In certain embodiments, a needleless connector replaces thebag spike 22 to connect to IV bags equipped with the appropriate matingneedleless connector. The IV set 20 includes a check valve 23 and twoneedleless access ports 15, configured to allow fluidic connection ofanother fluid device or tube having an appropriate needleless connectorto the IV set 20. In certain embodiments, the needleless connector 15comprises a female Luer connector. The IV set 20 also includes a pumpingsegment 26 configured to mate with a peristaltic IV pump (not shown inFIG. 1B). The pumping segment 26 includes a resilient tube and locatingfittings configured to place the resilient tube beneath the fingers ofperistaltic pumping mechanism, such as shown in FIGS. 2A and 2B. Theresilient tube is described in greater detail with respect to FIG. 3 .The IV set also includes a needleless fitting 28 configured to connectto an infusion device (not shown), for example an IV cannula, adapted tointroduce the medical fluid delivered through the IV set 20 into thebody of the patient 10. All of the fittings and elements of IV set 20are connected by tubing 24. In certain embodiments, the IV set 20includes additional fittings, such as a manual flow control device. Incertain embodiments, the IV set 20 does not include one or more of theelements shown in FIG. 1B. In certain embodiments, the IV set 20comprises additional lines connected to one of the tubes 24 through aY-fitting (not shown). In certain embodiments, one or more of theelements shown in FIG. 1B are replaced by other elements serving thesame function.

FIGS. 2A and 2B are a perspective view and a cross-section view,respectively, of a peristaltic pumping mechanism 34A according tocertain aspects of the present disclosure. In certain embodiments, theperistaltic pumping mechanism 34A is a part of the pump module 34 ofFIG. 1A. The peristaltic pumping mechanism 34A comprises a series ofcams 40 fixedly mounted on a shaft 42 that is rotated by a motor (notshown). In certain embodiments, the shaft 42 rotates at a constantspeed. In certain embodiments, the shaft 42 rotates at a speed thatvaries over a single rotation. In certain embodiments, each of the cams40 presses on followers or “fingers” 44 that are in contact withadjacent sections of the tube 26A of pumping segment 26. In certainembodiments, the portions of the fingers 44 that contact the tube 26Aare curved in the direction perpendicular to the length of the tube. Incertain embodiments, the same portions of the fingers that contact thetube 26A are flat in the direction perpendicular to the length of thetube. As each finger 44 descends, when displaced by rotation of therespective cam 40, the tube 26A is compressed between the finger 44 anda platen 46. The locating fittings of pumping segment 26 have beenomitted in FIG. 2A so as not to obscure the disclosure, but serve tolocate the tube 26A beneath the fingers 44.

FIG. 2B illustrates how the peristaltic motion of the fingers 44 forcesfluid through the tube 26A so as to deliver the medical fluid to thepatient 10. The fingers 44 move up and down, in the view of FIG. 2B, ina synchronized manner such that each adjacent finger 44 is a step aheadof the finger 44 on one side and a step behind the finger 44 on theother side. At the moment in time captured in FIG. 2B, the tube 26A hasbeen pinched shut at two points 54A and 54B. A pocket of fluid 52 hasbeen formed by the rebound of the tube 26A. As the fingers 44 directlyover points 54A and 54B ascend and the fingers 44 to the immediate leftof the ascending fingers 44 descend, the pocket 52 will move to theleft. As this wave-like motion continues, the pocket 52 will be moved tothe exit 50 of the pumping mechanism 34A and new pockets will have beenformed and moved along in the same fashion. In this manner, aperistaltic pumping mechanism periodically delivers an amount of fluidequal to the volume of pocket 52. The time interval at which the pockets52 of fluid are delivered is controlled by the rate of rotation of shaft42.

The volume of pocket 52 is affected by the resilience of the tube 26A.If the tube 26A initially rebounds to a first shape having a firstcross-sectional area and later, for example after a certain amount ofuse in an IV pump, the material of tubing 26A becomes fatigued and onlyrebounds to a second cross-sectional area that is less than the firstarea, then the volume of pocket 52 is lower than it was initially whenthe tube 26A was new. The amount of reduction in rebound may beinfluenced by the amount of overcompression of the tube 26A.

FIG. 3 is a perspective view of a standard round tube 26A as used inexisting IV sets 20. The tube 26A has an interior passage 53 with aninterior surface 51 that is circular in profile. The tube wall 56 is ofuniform thickness both around the cross-section and along the length ofthe tube 26A.

FIGS. 4A and 4B are cross-sectional view of the tube 26A of FIG. 3 beingmanipulated by one of the peristaltic pumping fingers of FIGS. 2A and2B. FIG. 4A depicts the configuration of the tube 26A and the finger 44and platen 46 when the finger 44 is in the fully “up” or “open”position. The tube 26A is in its fully expanded shape wherein theinterior passage 53 has the largest cross-sectional area.

FIG. 4B depicts the configuration of the tube 26A when the finger 44 hasdescended and is compressing the tube 26A against the platen 46. The topportion of the interior surface 51 is touching the bottom portion of thesame surface 51 in the middle of the tube 26A. Two gaps 60 remain at theedges of the interior passage 53 where the tube wall 56 has not beendeformed sufficiently to form a sharp crease in the interior surface 51.The gaps 60 are sometimes referred to as “weeping” openings. Closingthese gaps 60 requires sufficient force to distort the walls 56 and forma sharp crease in the interior surface 53 at the edges of the gaps 60.

Materials such as silicone have been used for the tube 26A in pumpingsegments 26 because silicone retains its resilience after repeatedcycles of compression sufficient to distort the tube walls 46 andthereby form a liquid tight seal across the tube 26A. There is a desireto move away from silicones as materials in IV sets for reasons of costreduction and the relatively high gas permeability of silicone withrespect to other elastomers. Possible materials for use in pumpingsegments include thermoplastic elastomers such as polyurethane,ultra-high-weight polyvinyl chloride, and polyesters. Some of thesematerials, however, do not exhibit the resilient and reboundcharacteristics of silicone and therefore do not provide sufficientoperational life under the levels of overcompression typically used withsilicone tubes. Use of these materials is possible with a reduced levelof compressive force that results in the reduction or elimination ofovercompression of the material of the tube 26A.

FIG. 5A is a cross-sectional view of a low-force pumping segment 26Baccording to certain aspects of the present disclosure. The interiorpassage 74 has a generally oval shape with, in this embodiment, twonotches 76A, 76B on opposite sides of the interior surface 80. Thenotches 76A, 76B separate the interior surface 80 into a first surface80A and a second surface 80B. Each notch 76A, 76B has a respective tip78A, 78B. The surfaces 80A and 80B approach each other asymptotically asthe surfaces 80A, 80B near the tips 78A, 78B. The surfaces 80A, 80B meetand are sealed to each other at the tips 78A, 78B. The wall 72 of tube26B has a first region 72A between the tips 78A, 78B on the side ofinterior surface 80A and a region 72B between the tips 78A, 78B on theside of interior surface 80B. Wall region 72A has a constant orsubstantially constant thickness T1 and wall region 72B has a constantor substantially constant wall thickness T2. In certain embodiments, thethicknesses T1 and T2 are equal. In certain embodiments, the interiorsurfaces 80A and 80B are of equal cross-section length D along thesurfaces as indicated by the dashed-line arrow for surface 80A.

In certain embodiments, tube 26B is extruded with a shaped profile toform the notches 76 and tips 78. In certain embodiments, two separatesheets (not shown) form the first and second wall regions 72A and 72Band are bonded on both sides such that the edge of the bonded areasforms the tips 78.

FIGS. 5B and 5C are cross-sectional views of the pumping segment 26B ofFIG. 5A being manipulated by one of the peristaltic pumping fingers 44of FIGS. 2A and 2B according to certain aspects of the presentdisclosure. FIG. 5B depicts the pumping segment 26B in the fully openposition with the interior passage 74 having its maximum cross-sectionalarea. In certain embodiments, the first and second wall regions 72A, 72Bare in contact only at the tips 78A, 78B when in the fully openposition. In certain embodiments, the walls 72A, 72B are in continuousgapless contact from the tips 78A, 78B at least a portion of a distancetowards a center of the tube 26B when in the fully open position.

As the finger 44 descends towards platen 46, the tube 26B is compressedbetween the finger 44 and platen 46. As the first wall region 72A isdisplaced towards the second wall region 76B, the length of thecontinuous gapless contact between the interior surfaces 80A and 80Bextending from the tips 78A, 78B is increased in proportion to thedisplacement. FIG. 5C depicts the configuration of the tube 26B when thefinger 44 has displaced the first wall region 72A sufficiently such thatthe interior surfaces 80A and 80B are in continuous gapless contact fromtip 78A to tip 78B.

Where the prior art circular tube 26A formed gaps 60 at the ends of thecontact between surfaces 51 in FIG. 4B, the tips 78A, 78B of tube 26Bprovide the sharp creases required to seal the contacting surfaces 80A,80B without the need for the level of compressive force required toclose the gaps 60 of a round tube 26A. In certain embodiments, thefinger 44 of FIG. 5C descends sufficiently so as to form a gap betweenthe finger 44 and platen 46 that is approximately equal to the sum ofthe respective thicknesses T1, T2 of the first and second wall portions72A and 72B. In certain embodiments, it may be necessary to overcompressthe tube 26B by a small amount, for example 2% of the sum of therespective thicknesses of the first and second portions 72A and 72B, inorder to compensate for variation in wall thickness or surfacesmoothness of the inner surfaces 80A, 80B. In certain embodiments, thefinger 44 of FIG. 5C descends sufficient to form a gap between thefinger 44 and platen 46 that is approximately equal to 5% less than thesum of the thicknesses T1 and T2. In certain embodiments, the amount offorce applied by the finger 44 to tube 26B is limited to the forcesufficient to bring the interior surfaces 80A, 80B into continuousgapless contact across the entire distance between tips 78A and 78B. Incertain embodiments, the amount of force applied by the finger 44 totube 26B is limited to a force 10% greater than the force determined tobe sufficient to bring the interior surfaces 80A, 80B into continuousgapless contact across the entire distance between tips 78A and 78B. Incertain embodiments, the amount of force applied by the finger 44 totube 26B is limited to the force 25% greater than the force determinedto be sufficient to bring the interior surfaces 80A, 80B into continuousgapless contact across the entire distance between tips 78A and 78B.

FIG. 6 is another embodiment of a low-force pumping segment 26Caccording to certain aspects of the present disclosure. In certainembodiments, tube 26C has the same shape and features as tube 26B ofFIG. 5A. Additionally, in certain embodiments, one or more springelements 82 are coupled to the exterior of the tube wall 72 to provideat least a portion of the rebound characteristics required for the tube26C to fully open when the compressive force is removed. In certainembodiments, two spring elements 82 are respectively coupled to thefirst and second wall regions 72A, 72B. In certain embodiments, thematerial of tube walls 72 are not resilient and form only a sealedpassage 74 to contain the fluid. The tube wall 72 of FIG. 6 has the sameprofile as FIG. 5A with notches 76 and tips 78.

FIG. 7 is another embodiment of a low-force pumping segment 26Daccording to certain aspects of the present disclosure. In certainembodiments, at least one coupling element 92 is coupled to the exteriorof tube wall 72. In certain embodiments, two coupling elements 92A and92B are coupled to the first and second wall regions 72A and 72B. Thecoupling elements are configured to couple to a pumping mechanism and bedrawn apart by the pumping mechanism thereby separating the first andsecond wall regions 72A and 72B of the tube 26D. In certain embodiments,the coupling element 92 is magnetic and a magnetic driver (not shown) ofthe pumping mechanism attracts the magnetic coupling elements 92A, 92Band draws them apart as the finger 44 retracts. In certain embodiments,the coupling elements 92A, 92B have mechanical attachment features, suchas Velcro®, that provide sufficient coupling strength to cause the wallsregions 72A, 72B to separate during use while still being removable fromthe pumping mechanism 34A.

The disclosed low-force pumping segment provides an improved ability toshut off flow through the pumping segment by compression of the tube ofthe pumping segment using a reduced amount of force, compared to theforce required to shut off flow though a circular tube. In certainembodiments, the tube of the low-force pumping segment has a pair ofnotches on opposite sides of the interior surface. The notches areshaped such that the surfaces on each side of the notch approach eachother approximately asymptotically and come to a tip where the surfacesare sealingly joined. The shape of the gap between the two surfaces nearthe tip are configured such that the surfaces are in continuous andsealing contact with each other from each tip to points of first contacttowards the center of the tube, wherein the points of contact on eachside advance towards the center as the tube is compressed.

It is understood that the specific order or hierarchy of steps or blocksin the processes disclosed is an illustration of exemplary approaches.Based upon design preferences, it is understood that the specific orderor hierarchy of steps or blocks in the processes may be rearranged. Theaccompanying method claims present elements of the various steps in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims.

Reference to an element in the singular is not intended to mean “one andonly one” unless specifically so stated, but rather “one or more.”Unless specifically stated otherwise, the term “some” refers to one ormore.

Pronouns in the masculine (e.g., his) include the feminine and neutergender (e.g., her and its) and vice versa. All structural and functionalequivalents to the elements of the various aspects described throughoutthis disclosure that are known or later come to be known to those ofordinary skill in the art are expressly incorporated herein by referenceand are intended to be encompassed by the claims. Moreover, nothingdisclosed herein is intended to be dedicated to the public regardless ofwhether such disclosure is explicitly recited in the claims. No claimelement is to be construed under the provisions of 35 U.S.C. § 112,sixth paragraph, unless the element is expressly recited using thephrase “means for” or, in the case of a method claim, the element isrecited using the phrase “operation for.”

Although embodiments of the present disclosure have been described andillustrated in detail, it is to be clearly understood that the same isby way of illustration and example only and is not to be taken by way oflimitation, the scope of the present invention being limited only by theterms of the appended claims.

What is claimed is:
 1. A medical-grade tube, comprising: a pumpingsegment having an exterior surface; a first magnetic coupling elementcoupled to a first portion of the exterior surface; and a secondmagnetic coupling element coupled to a second portion of the exteriorsurface, the first and second magnetic coupling elements configured tomagnetically couple to a pumping mechanism and be drawn apart by thepumping mechanism for separating the first and second portions of thetube.
 2. The medical-grade tube of claim 1, the pumping segment furthercomprising an interior surface comprising a first notch and a secondnotch on opposite sides of the interior surface such that the first andsecond notches divide a wall of the pumping segment into a first wallregion and a second wall region and divide the interior surface into afirst interior surface and a second interior surface respectivelyforming interior surfaces of the first wall region and the second wallregion.
 3. The medical-grade tube of claim 2, wherein the first andsecond portions of the exterior surface are separated respectively fromthe first and second interior surfaces by respective thicknesses of thefirst and second wall regions.
 4. The pumping segment of claim 2,wherein: each notch of the first and second notches comprises arespective tip; and the first interior surface and the second interiorsurface asymptotically approach each other at each notch and sealinglymeet at the tip of each notch.
 5. The pumping segment of claim 2,wherein the first and second interior surfaces have equal widths.
 6. Thepumping segment of claim 2, wherein the notches are configured such thatthe first and second interior surfaces are in continuous gapless contactfrom the tips at least a portion of a distance towards a center of thetube when the first wall region of the tube is displaced toward thesecond wall region.
 7. The pumping segment of claim 6, wherein: thefirst and second wall regions of the tube have constant respective wallthicknesses between the tips of the notches; and the first and secondinterior surfaces are in continuous gapless contact between the tipswhen the tube is compressed to a total thickness approximately equal toa sum of the respective thicknesses of the first and second wallregions.
 8. The pumping segment of claim 2, wherein the tube isconfigured to elastically deform as the first wall region of the tube isdisplaced toward the second wall region and to separate the first wallregion of the tube from the second wall region of the tube as the tubereturns to an undeformed shape.
 9. The pumping segment of claim 1,wherein the tube comprises a thermoplastic elastomer, a polyurethane, anultra-high-weight polyvinyl chloride, a polyester, or a silicone. 10.The pumping segment of claim 1, wherein the pumping segment comprises anextruded tube.
 11. The pumping segment of claim 1, wherein the pumpingsegment comprises a pair of edge bonded sheets.
 12. An intravenous (IV)set with a low shut-off force, the IV set comprising: a medical-gradetube for delivering medical fluid, the tube having a first magneticcoupling element coupled to a first portion of an exterior surface ofthe medical-grade tube, and a second magnetic coupling element coupledto a second portion of the exterior surface; and a pumping mechanism,wherein the first and second magnetic coupling elements are configuredto magnetically couple to the pumping mechanism, and wherein the pumpingmechanism is configured to magnetically act upon and draw apart thefirst and second magnetic coupling elements.
 13. The IV set of claim 12,the tube further comprising an interior surface comprising a first notchand a second notch on opposite sides of the interior surface such thatthe first and second notches divide a wall of the tube into a first wallregion and a second wall region and divide the interior surface into afirst interior surface and a second interior surface respectivelyforming interior surfaces of the first wall region and the second wallregion.
 14. The IV set of claim 13, wherein the first and secondportions of the exterior surface are separated respectively from thefirst and second interior surfaces by respective thicknesses of thefirst and second wall regions.
 15. The IV set of claim 13, wherein: eachnotch of the first and second notches comprises a respective tip; andthe first interior surface and the second interior surfaceasymptotically approach each other at each notch and sealingly meet atthe tip of each notch.
 16. The IV set of claim 13, wherein the first andsecond interior surfaces have equal widths.
 17. The IV set of claim 13,wherein the notches are configured such that the first and secondinterior surfaces are in continuous gapless contact from the tips atleast a portion of a distance towards a center of the tube when thefirst wall region of the tube is displaced toward the second wallregion.
 18. The IV set of claim 17, wherein: the first and second wallregions of the tube have constant respective wall thicknesses betweenthe tips of the notches; and the first and second interior surfaces arein continuous gapless contact between the tips when the tube iscompressed to a total thickness approximately equal to a sum of therespective thicknesses of the first and second wall regions.
 19. The IVset of claim 13, wherein the tube is configured to elastically deform asthe first wall region of the tube is displaced toward the second wallregion and to separate the first wall region of the tube from the secondwall region of the tube as the tube returns to an undeformed shape. 20.A medical-grade tube prepared by a process comprising the steps of:providing a pumping segment having an exterior surface; coupling a firstmagnetic coupling element to a first portion of the exterior surface;and coupling a second magnetic coupling element to a second portion ofthe exterior surface, wherein the first and second magnetic couplingelements are configured to magnetically couple to a pumping mechanismand be drawn apart by the pumping mechanism for separating the first andsecond portions of the tube.